Organic EL (Electro-Luminescence) display devices start being put into practical use. One feature of an organic EL display device is being flexible. An organic EL display device includes, in each of pixels, at least one organic EL element (Organic Light Emitting Diode: OLED) and at least one TFT (Thin Film Transistor) controlling an electric current to be supplied to each of the at least one OLED). Hereinafter, an organic EL display device will be referred to as an “OLED display device”. Such an OLED display device including a switching element such as a TFT or the like in each of OLEDs is called an “active matrix OLED display device”. A substrate including the TFTs and the OLEDs will be referred to as an “element substrate”.
An OLED (especially, an organic light emitting layer and a cathode electrode material) is easily influenced by moisture to be deteriorated and to cause display unevenness. One technology developed in order to provide an encapsulation structure that protects the OLED against moisture while not spoiling the flexibility of the OLED display device is a thin film encapsulation (TFE) technology. According to the thin film encapsulation technology, an inorganic barrier layer and an organic barrier layer are stacked alternately to form a thin film that provides a sufficiently low water vapor transmission rate (WVTR). From the point of view of moisture-resistance reliability of the OLED display device, such a thin film encapsulation structure is typically required to have a WVTR lower than, or equal to, 10−4 g/m2/day.
A thin film encapsulation structure used in OLED display devices commercially available currently includes an organic barrier layer (polymer barrier layer) having a thickness of about 5 μm to about 20 μm. Such a relatively thick organic barrier layer also has a role of flattening a surface of the element substrate. However, such a thick organic barrier layer involves a problem that the bendability of the OLED display device is limited.
There is also a problem that the mass-productivity is low. The relatively thick organic barrier layer described above is formed by use of a printing technology such as an inkjet method, a microjet method or the like. By contrast, an inorganic barrier layer is formed by a thin film deposition technology in a vacuum atmosphere (e.g., lower than, or equal to, 1 Pa). The formation of the organic barrier layer by use of a printing method is performed in the air, whereas the formation of the inorganic barrier layer is performed in vacuum. Therefore, the element substrate is put into, and out of, a vacuum chamber during the formation of the thin film encapsulation structure, which decreases the mass-productivity.
Under such a situation, as disclosed in, for example, Patent Document 1, a film formation device capable of producing an inorganic barrier layer and an organic barrier layer continuously has been developed.
Patent Document 2 discloses a thin film encapsulation structure including a first inorganic material layer, a first resin member and a second inorganic material layer provided in this order, with the first inorganic material layer being the lowest layer among the three layers. In this thin film encapsulation structure, the first resin member is present locally, more specifically, around a protruding portion of the first inorganic material layer (first inorganic material layer covering a protruding portion). According to Patent Document 2, the first resin member is present locally, more specifically, around the protruding portion, which may not be sufficiently covered with the first inorganic material layer. With such a structure, entrance of moisture or oxygen via the non-covered portion is suppressed. In addition, the first resin member acts as an underlying layer for the second inorganic material layer. Therefore, the second inorganic material layer is properly formed and properly covers a side surface of the first inorganic material layer with an expected thickness. The first resin member is formed as follows. An organic material heated and gasified to be mist-like is supplied onto an element substrate maintained at a temperature lower than, or equal to, room temperature. As a result, the organic material is condensed and put into liquid drops on the substrate. The organic material in liquid drops moves on the substrate by a capillary action or a surface tension to be present locally, more specifically, at a border between a side surface of the protruding portion of the first inorganic material layer and a surface of the substrate. Then, the organic material is cured to form the first resin member at the border. Patent Document 3 also discloses an OLED display device including a similar thin film encapsulation structure.